Non iPhone users for Apple Watch

The Apple Watch is an iPhone accessory, and needs an iPhone

It is possible to use an Apple Watch in a limited capacity if there is an iPhone in the family, and the cellular carrier supports the Apple Watch Family Plan

https://www.apple.com/newsroom/2020/09/apple-extends-the-apple-watch-experience-to-the-entire-family/

https://support.apple.com/en-us/HT211768

You are able to purchase an Apple Watch without an iPhone, but all Apple Watches require an iPhone to operate - so you would need an iPhone to be able to use the watch.